This invention relates to a foundation improvement process and an apparatus thereof for improving a foundation by jet-injecting a hardening agent in the ground in order to stabilize a soft and weak foundation.
Conventionally, there is known a foundation improvement process which is disclosed in Japanese Patent Publication (Tokkyo Koho) No. 58(1983)-27364. According to this prior art, improvement of a foundation is performed in the following manner. That is, an injection rod including three flow passages is formed at its lower side wall with a third nozzle communicating with a third flow passage, and spacedly thereabove with a first nozzle communicating with a first flow passage, and a second nozzle encircling the first nozzle and communicating with a second flow passage. And, while pressure-feeding a fresh water to the first and second flow passages, and air to the second flow passage, the injection rod is rotatingly descended into an objective foundation. A jet water jetted from the third nozzle is used as a lubrication liquid and for forming a slurry area. Similarly, jet water jetted from the first nozzle and air encircling the jet water from the second nozzle grind the foundation and at the same time, form the slurry area. Furthermore, due to the air lift effect of the air jetted from the second nozzle, slurry including viscous soil is discharged on the earth. The jet fresh water of the third nozzle is switched over to a hardening agent at a time when the digging degree reaches a predetermined depth, and the rod is lifted while maintaining the jetting of the first and second nozzles. And, while lifting the rod, the hardening agent is injected in the ground for improving the foundation.
However, the conventional process set forth above has the disadvantage that when the rod is lifted while injecting the hardening agent, a part of the hardening agents which was jet-injected in the foundation from the third nozzle is discharged on the earth due to the air lift effect of the fresh water and the air jetting from the first and second nozzles.